Kinetics of the reaction over the temperature rangeHO 2 + BrO 233 – 348

The reaction is the rate-limiting step in a key catalytic ozone destruction cycle in the lower stratosphere. BrO] 2 ] products In this study a discharge-Ñow reactor coupled with molecular beam mass spectrometry has been used to study the BrO ] 2 reaction over the temperature range 233È348 K. Rate constants were measured under pseudo-Ðrst-order conditions in separate experiments with Ðrst and then BrO in excess in an e†ort to identify possible complications in the reaction conditions. At 2 298 K, the rate constant was determined to be (1.73^ 0.61)] 10~11 cm3 molecule~1 s~1 with in excess and 2 (2.05^ 0.64)] 10~11 cm3 molecule~1 s~1 with BrO in excess. The combined results of the temperature-dependent experiments gave the following Ðt to the Arrhenius expression : k \ (3.13^ 0.33)] 10~12 exp(536^ 206/T ) where the quoted uncertainties represent two standard deviations. The reaction mechanism is discussed in light of recent ab initio results on the thermochemistry of isomers of possible reaction intermediates.